Just hours ago, Michael Phelps finished his last race as a competitive swimmer. It was the men's 4x100 meter medley relay. Phelps was one of four swimmers racing for team USA, which was heavily favored to win the gold. A quick word now. If you're waiting to watch the results on prime time tonight, you may want to turn the volume down because we're going to NPR's Howard Berkes now in London who was at that race this evening.

Howard, unbelievable. The U.S. team took the gold. Michael Phelps' 18th career gold medal. Tell us about the race.

HOWARD BERKES, BYLINE: Well, it was an amazing race. You had Matthew Grevers start out in the backstroke on world record pace. Then the United States had lost its lead in the breaststroke. Michael Phelps came in with the butterfly, regained the lead. And then Adrian Nathan in the freestyle leg just blew them out of the water, finished a body length ahead, a clear no-question gold medal. For a race, you know, that the United States team has won every Olympics it's ever competed in in this event, great way to cap Michael Phelps' career.

RAZ: We know that his mother was in the stands cheering him on. What was it like? What was the atmosphere like inside the building during that race?

BERKES: Oh, the place was just rocking. The noise was deafening. And, you know, there were some Americans there for sure, but people from all the countries that were there to see the other swimmers were also cheering. I think everybody wanted to see Michael Phelps go out with something memorable. They were there to see it. There was a lot of excitement at being a witness to history.

RAZ: He is leaving swimming now with a total of 22 Olympic medals, 18 gold medals. Incredible. What's next for him?

BERKES: Well, by the way, those aren't just swimming records. Those are records for any Olympic athlete ever. He is the most decorated Olympic athlete ever to compete in the Olympics, and there's no one anywhere near close who's competing today. These are records that are likely to stand for a long time. And all we've heard so far about what his plans are next, he said that he's definitely getting out of the pool. He's not going to swim in any kind of competitive races at all.

He says what he wants to do is travel, which is what, you know, a lot of us want to do when we retire. He's only 27. It's not a full retirement, but he said he wants to travel. He wants to see the world. He wants to see the world, I think, other than from a hotel that he's staying in to get into a pool, you know, the next day. And that's what he's - that's all he's said so far about what he plans to do.

RAZ: Howard, another piece of history made today with Oscar Pistorius, a double amputee running in an Olympic race. Tell us about that one.

BERKES: That was also an amazing sight. Eighty thousand people in the stadium on their feet roaring and cheering when his name was announced. He ran in a early heat of the 400 meters and he qualified. And he runs on these carbon fiber legs called blades, and it's a really otherworldly kind of sight. He's an amazing athlete. There's some controversy about whether he should be competing in the Olympics, but he did meet the qualifying time. And he ran, you know, he ran faster today than almost half the field that ran.

So he'll be in the semifinals tomorrow. It would be a surprise if he made it into the finals, but he did - he's already made history. He's very happy about it, and people are very excited to see this barrier broken at the Olympics.

RAZ: That's NPR's Howard Berkes reporting on the Olympics for us from London. Howard, thanks.